1. Field of the Invention
The invention is generally related to the use of a remotely operated vehicle (ROV) or robotic tooling for underwater work and more particularly to the means used for launching, controlling, and recovering an ROV or tooling package.
2. General Background
Many underwater operations, such as drilling for and production of oil and gas, installation and maintenance of offshore structures, or laying and maintaining underwater pipelines require the use of a remotely operated vehicle (ROV) or robotic tooling.
The deployment of an ROV is typically achieved by launching the unit from either a bottom founded or floating host platform, a dynamically positioned marine vessel dedicated specifically for the purpose of supporting an ROV, e.g. an ROV support vessel (RSV), or any such surface vessel with sufficient size and characteristics that provide a suitably stable platform for the launching and recovery of an ROV.
Both bottom founded and floating host platforms are fixed in position at the site and are normally engaged in collateral activities such as drilling and offshore production or construction. Thus, the operations of the ROV are limited according to the distance that the ROV can travel from the host platform as well as by restrictions in operating periods due to the collateral activities of the host platform.
In the case of dedicated vessel deployment such as an RSV, significant costs are associated with operation of a fully founded marine vessel and its mobilization to and from the ROV work site. Typically, a dedicated RSV may have a crew of twenty and a considerable cost not directly related to the operation of the ROV.
ROV operation and monitoring is controlled from the host platform or RSV by means of an umbilical line between the host platform or RSV and the ROV. It can be seen from this that the operational distance of the ROV is directly related to the length of the umbilical line.
A remotely operated near surface drone vessel with adequate stability that is capable of launching, controlling, and recovering an ROV eliminates the limitations associated with operation from a fixed host platform and reduces the expense associated with a manned, dedicated RSV.
The remotely operated drone vessel requires an umbilical line, storage drum, and winch to launch, control, and recover the ROV. The drone vessel must have certain compartments that are dedicated to electronic control equipment that must remain dry. Locating the winch and storage drum for the umbilical line in a dry compartment requires a seal that the umbilical line must pass through. Failure of the seal would allow water into the compartment, which would cause damage to any equipment in the compartment. A sealed compartment also adds buoyancy, which requires additional ballast, thereby increasing the mass and possibly the size of the vessel, which is undesirable.
Storage of the umbilical in a dry compartment requires a large volume of variable ballast in order to maintain a constant operating draft. The dispensing of the umbilical from a dry compartment and suspending into the sea will result in an increase in the displacement of the combined vessel, umbilical system. This change in displacement will not occur when using a flooded umbilical compartment. The use of large volumes of variable ballast is undesirable as it increases the operation complexity, the mass, and the size of the vessel. It can be seen that water displacement and ballast are not adequately addressed in the present art.
The invention addresses the above needs. What is provided is a drone vessel for an ROV. The drone vessel utilizes dynamic positioning. The drone vessel is remotely controlled by radio telemetry, preferably modular in construction, and may be semi-submersible. The vessel contains a radio telemetry package, one or more generators, an umbilical winch for lowering and raising an ROV, space for receiving and storing an ROV, and ballast control. The central compartment in the drone vessel is free flooding and houses the drum for storing umbilical line and the winch for paying out umbilical line to the ROV. The center section, winch, or ballast may be movable in order to improve the vessel stability when stationary or maneuvering at low speeds. The central compartment also includes space for the ROV.